The present invention relates generally to the field of optical data discs, and in particular, to a hubless optical disc having a low radial runout error and method of manufacturing such a disc.
Optical data discs are a popular media choice for the distribution, storage and accessing of large volumes of data. This includes audio and video program material, as well as computer programs and data. Formats of optical data discs include audio CD (compact disc), CD-R (CD-readable), CD-ROM (CD-read only memory), DVD (digital versatile disc or digital video disc) media, DVD-RAM (random access memory), various types of rewritable media, such as magneto-optical (MO) discs, and phase change optical discs. In general, optical discs (such as CD-ROMs) are produced by making a master which has physical features representing the data formed in or on a reference surface therein. The master is used to make a stamper, which, in turn, is used to make production quantities of replica discs, each containing the data and tracking information which was formed in the master. The high data capacity, convenience, and relatively low production costs of such discs have contributed to their great success and acceptance in the marketplace.
In optical discs, data is stored as a series of lower reflectance xe2x80x9cpitsxe2x80x9d embossed within a plane of higher reflectance xe2x80x9clandsxe2x80x9d. The microscopic pits are formed on the surface of the plastic disc when the material is injected into a mold. Typically, the pitted side of the disc is then coated with a reflectance layer, such as a thin layer of aluminum, and in the case of a CD, followed by a protective layer of lacquer. The pits on an optical disc can be arranged in a spiral track originating at the disc center hub and ending at the disc outer rim. The data can also lie in a series of concentric tracks spaced radially from the center hub.
To read the data on an optical disc, an optical disc player shines a small spot of laser light through the disc substrate onto the data layer as the disc rotates. The intensity of the light reflected from the disc""s surface varies according to the presence (or absence) of pits along the information track. When a pit lies directly underneath the xe2x80x9creadoutxe2x80x9d spot, much less light is reflected from the disc than when the spot is over a flat part of the track. A photodetector and other electronics inside the player translate this variation into the 0s and 1s of the digital code representing the stored information.
As optical disc technology has evolved, optical discs have increased in storage capacity. Higher density discs have resulted in the storage of a greater amount of information within the same size of disc area. For example, a CD having a storage capacity of 0.65 gigabytes has data pits which are 0.83 xcexcm long and has a track pitch (the distance between data tracks) of approximately 1.6 xcexcm. In comparison, a DVD disc data pit is as small as 0.4 xcexcm long, and a track pitch of only 0.74 xcexcm, resulting in a storage capacity of 5 gigabytes on a single layer. Similarly, MO and phase change disc track pitch varies with the density or storage capacity of the disc.
To read high capacity optical discs having smaller pits and a smaller track pitch, the optical disc player""s read beam must achieve a smaller spot focus. Further, data must be more precisely located on the optical disc substrate. Ideally, the data tracks are concentrically located about the center hole of the disc. During the optical disc manufacturing process, a centering error is introduced into the radial positioning of the data tracks (or track cycles) on the optical disc. This error is known as radial total indicated runout (RTIR). RTIR is defined as the measure of non-concentricity of the data tracks to the drive spindle on the optical disc player.
In a conventional optical disc manufacturing process, RTIR error is introduced during the injection molding process. The injection molding process begins with a tooling mechanism. The optical tooling mechanism includes a fixed side and a moving side. The moving side typically includes a stamper for replicating data and format information into the disc substrate, and a movable gate cut for cutting a central opening in these disc substrates. The stamper is located by an inner holder, wherein the inner holder fits over the stamper. Several more parts are located at the center inside diameters of the tool. In typical optical tooling, all of these parts need to remain concentric between the gate cut and the removable inner holder for concentric registration (or centering) of the format information in the disc substrate relative to the central opening or central hole.
In a disc molding process, a resin, typically polycarbonate, is forced in through a sprue channel into a substrate cavity within the optical tooling (mold) to form the optical disc substrate. The format of the grooves and pits are replicated in the substrate by the stamper as the cavity is filled. After filling, the gate cut is brought forward to cut a center hole in the optical disc. After the part has sufficiently cooled, the optical tooling mold is opened and the sprue and product eject are brought forward for ejecting the formed optical disc off of the stamper. The inner holder may be removed to allow change out of the stamper.
Any misalignment of the aforementioned optical tooling results in the replication of greater RTIR error in the molded disc. Further, any debris, flash or other imperfections resulting from the gate cut action, and any misalignment of the moving stamper relative to the fixed side of the optical tooling will add to the RTIR error. When track pitch is larger, such as in CD optical discs, the disc reader will read CD optical discs having typical RTIR errors between 50 and 100 xcexcm due to a relatively large track pitch (1.6 xcexcm). For higher capacity discs, such as DVD discs, it is difficult (or impossible) for an optical reader to read a DVD optical disc having an RTIR error greater than 50 xcexcm, due to the smaller track pitch. Similar problems exist with MO disc technology having a typical RTIR between 20 and 30 xcexcm.
In order to reduce the RTIR error to acceptable (or readable) levels, hubs are installed within the center opening of the optical disc. A new center is located, and the hub is installed centered on the disc relative to the formatted data tracks. This is typically accomplished using a costly centering process. Further, the hub itself is insert molded, resulting in a high expense relative to the total disc cost.
It is desirable to have a high density optical disc having a low RTIR error which does not require the use of a hub for centering the drive to the information on the disc. It is desirable to have a high density optical disc which may be mounted and centered on features molded into the plastic substrate of the disc. Further, it is desirable to have a disc molding process for forming high capacity optical discs which may include simple modifications to conventional optical tooling, and which introduces low RTIR error into the disc substrate.
The present invention includes a high-capacity optical disc having a low RTIR error and which does not require the use of a hub for centering the information on the disc. The present invention also includes a disc molding process for forming high capacity optical discs which includes optical tooling which introduces low RTIR error into the disc substrate.
In one embodiment, the present invention includes a hubless optical disc for storage of information therein. The optical disc includes a disc substrate having a formatted surface and a central portion, wherein the formatted surface includes a plurality of generally concentric tracks, and wherein each track can be defined as a concentric ring or a cycle of a spiral track, and wherein the central portion is proximate the center of the disc substrate, and the formatted surface surrounds the central portion. A disc alignment mechanism is located within the central portion, such that the concentric registration of the formatted information is specified relative to the disc alignment mechanism. The disc alignment mechanism may be integrally molded within the disc substrate or formed separate from the disc substrate and coupled to the disc substrate.
The disc alignment mechanism may be matable with an optical disc player drive spindle. The disc alignment mechanism may include an annular groove in the disc substrate, an annular ridge extending from the disc substrate, or a plurality of holes in the disc substrate. The optical disc may further include a central hole within the disc substrate, wherein the central hole extends through the central portion of the disc substrate. The optical disc may further include means for aiding and coupling the optical disc to an optical disc player drive spindle, wherein the means for coupling is secured across the opening.
In another embodiment, the present invention includes a hubless optical disc capable of storage of a high capacity of information, the hubless optical disc having a low radial total indicated runout error. The hubless optical disc includes a generally disc shaped substrate having a central hole. The disc substrate includes a formatted information area in a central portion, wherein the central portion is located between the central hole and the formatted disc substrate. Means are located within the central portion for concentric registration of the formatted information, including a disc alignment mechanism, wherein the concentric registration of the formatted information is specified relative to the disc alignment mechanism.
The means for concentric registration of the formatted information may be matable with an optical disc player drive spindle. The means for concentric registration may be integrally molded within the disc substrate or formed separate from the disc substrate and coupled to the disc substrate. The disc alignment mechanism may include an annular groove in the disc substrate, an annular ridge extending from the disc substrate, or a plurality of holes in the disc substrate. The optical disc may further comprise means for aiding and coupling the optical disc to an optical disc player drive spindle, wherein the means for coupling is secured across the opening.
In another embodiment, the present invention includes an optical disc capable of storage of a high capacity of information. The optical disc includes a disc substrate. A formatted surface is located within the disc substrate capable of containing data therein. The formatted surface includes a plurality of data tracks, the formatted surface having a track pitch of less than 0.74 xcexcm, and a low radial total indicated runout error of less than 50 xcexcm.
It is recognized that the formatted surface may have a track pitch of less than 0.74 xcexcm and a radial total indicated runout error of less than 30 xcexcm. In one preferred embodiment, the track pitch is 0.37 xcexcm or less.
Each data track may be defined as a cycle of a continuous spiral track, or each data track may be defined as a concentric track. The disc may have a capacity of greater than 20 gigabytes.
The disc substrate may include a disc alignment mechanism, wherein the concentric registration of the formatted information is specified relative to the disc alignment mechanism. The optical disc may include a central portion located between the center of the disc and the formatted surface, wherein the disc alignment mechanism is located within the central portion.
In another embodiment, the present invention includes a hubless optical storage system, including an optical disc drive and an optical media having a low radial total indicated runout. The optical media includes a disc substrate having a formatted surface in the central portion, wherein the central portion is proximate the center of the disc substrate and the formatted surface surrounds the central portion. A disc alignment mechanism is located within the central portion such that the concentric registration of the formatted information is specified relative to the disc alignment mechanism. The drive comprises a drive spindle having a mating mechanism for mating the drive with the optical media, the mating mechanism including a coupling mechanism formed on the drive spindle capable of mating with the disc alignment mechanism.
The disc alignment mechanism may include an annular ridge, and the coupling mechanism may include an annular groove capable of receiving the annular ridge. Alternatively, the coupling mechanism may include an annular ridge, and the disc alignment mechanism may include an annular groove capable of receiving the annular ridge.
The optical storage system may further include a mechanical hold-down, wherein the disc substrate is interposed between the drive spindle and the mechanical hold-down. The mechanical hold-down may apply a force normal to the disc substrate. Means are provided which are coupled to the mechanical hold-down for applying a force normal to the disc substrate. In one embodiment, the force is an electromagnetic force. The optical storage system may further include a vacuum mechanism for urging the disc substrate towards the drive spindle. The vacuum mechanism may include an opening in the drive spindle.
In another embodiment, the present invention includes a disc molding apparatus for forming an optical disc in a disc molding process. The disc molding apparatus includes a disc substrate cavity for forming a disc substrate therein. A sprue mechanism can be in fluid communication with the disc substrate cavity for allowing disc material to enter the disc substrate cavity. A removable stamper may be located on one side of the disc substrate cavity for forming formatted data into the disc substrate. Means may be provided for forming a disc alignment mechanism in the disc substrate, wherein the concentricity of the formatted data is specified relative to the disc alignment mechanism.
The means for forming a disc alignment mechanism may include an inner holder. The inner holder may be releasibly mounted adjacent the stamper for releasibly locking the stamper within the disc molding apparatus.
The inner holder may include a shape imparting mechanism for stamping the disc alignment mechanism into the disc substrate. The shape imparting mechanism may include an annular ring thereon, an annular depression located therein, or a plurality of registration pins extending therefrom. In one embodiment, the shape imparting mechanism also releasably locks the stamper within the disc molding apparatus. It is also recognized that the shape imparting mechanism may be located on the stamper or other disc molding apparatus part.
In another embodiment, the present invention includes a drive spindle for use in an optical disc drive assembly. The drive spindle includes a generally cylindrical shaped body. Means are coupled to the generally cylindrical shaped body for engaging an optical disc. The means for engaging having a mating mechanism, wherein the optical disc includes a formatted surface and a disc alignment mechanism. The concentricity of the formatted surface is specified relative to the disc alignment mechanism. The mating mechanism is engageable with the disc alignment mechanism.
A central hub may extend from the generally cylindrical shaped body for extending through a center opening in the optical disc. A flange may extend from the generally cylindrical shaped body, wherein the means for engaging an optical disc is coupled to the flange. The means for engaging may be formed integral the generally cylindrical shaped body. In one embodiment, the means for engaging may include an annular ring formed thereon, an annular groove formed therein, or a plurality of pins extending therefrom.